1. Technical Field
The invention relates to a vibrator, an oscillator, an electronic apparatus, a moving object, and a method of manufacturing a vibrator.
2. Related Art
In general, there are known electromechanical structures (e.g., a vibrator, a filter, a sensor, and an electric motor) provided with a mechanically movable structure called a micro electro mechanical system (MEMS) device formed using the semiconductor microfabrication technology. Among these examples, the MEMS vibrator is easy to manufacture so as to incorporate a semiconductor circuit, and is advantageous to miniaturization and sophistication compared to a vibrator and a resonator using an existing quartz crystal or dielectric body, and therefore the application range of the MEMS vibrator has been broadened.
As a representative example of MEMS vibrator of related art, there are known a comb-shaped vibrator and a beam-type vibrator, wherein the comb-shaped vibrator vibrates in a direction parallel to a surface of a substrate on which the vibrator is disposed, and the beam-type vibrator vibrates in a thickness direction of the substrate. The beam-type vibrator is a vibrator including a stationary electrode formed on the substrate, a movable electrode disposed so as to be separated from the substrate, and so on, and a clamped-free beam, a clamped-clamped beam, a free-free beam, and so on are known due to the way for supporting the movable electrode.
Since the free-free beam MEMS vibrator is supported by a support member at a part of the movable electrode thus vibrating, the part corresponding to a node of the vibration, a vibration leakage to the substrate is small, and the efficiency of the vibration is high. In the specification of U.S. Pat. No. 6,930,569 B2 (Document 1), there is proposed a technology of setting the length of the support member to a length appropriate to the frequency of the vibration to thereby improve the vibration characteristics.
Further, in JP-T-2004-515089 (Document 2), there is described a signal processing method asserted to be able to process the signal with low power consumption using a plurality of MEMS vibrators (vibrating micro-mechanical elements).
However, the MEMS vibrators described in Document 1 and Document 2 have a problem that it becomes difficult to obtain stable vibration characteristics or the desired vibration characteristics in the case of achieving further miniaturization. In the specific explanation, in a method of manufacturing a beam-type vibrator using the MEMS technology, there is generally adopted a method of stacking a sacrifice layer such as an oxide film as an upper layer of the stationary electrode formed on the substrate, and then removing the sacrifice layer after forming the movable electrode as an upper layer of the sacrifice layer to thereby separate the movable electrode from the substrate and the stationary electrode. Therefore, the movable electrode stacked as the upper layer part tends to have a shape reflecting the uneven shape of the lower layer part. For example, in the MEMS vibrator shown in FIG. 2 of Document 1 and the MEMS vibrator shown in FIG. 5a of Document 2 (partially extracted in accompanying FIGS. 2A and 2B), the pattern shape of the stationary electrode disposed in the lower layer appears as unevenness of the movable electrode in the upper layer. Such unevenness of the movable electrode exerts an influence on the stiffness of the movable electrode as a vibrating beam. Therefore, in the case of achieving further miniaturization of the vibrator, the influence becomes significant, and has caused a problem that it is unachievable to obtain the stable vibration characteristics and the desired vibration characteristics. More specifically, for example, even if the movable electrode (a vibrating beam) is disposed in a balanced manner in the plan view of the vibrator, since the unevenness of the pattern disposed in the lower layer is reflected, there is a case in which the uneven shape of the vibrating beam is off-balance in a side view. In this case, since the distribution of the stiffness in the vibrating beam is uneven, the balance of the vibration of the vibrating beam is lost, which leads the problem that the vibration efficiency is degraded, or the vibration leakage to the outside through the support section increases, as a result. Further, since the vibrating beam has such a complicated shape, there has been a problem that the vibration design in the case of manufacturing the vibrator becomes complicated.